The invention relates to a method for use in the manufacture of a building element of the type comprising a plate-shaped internal core member of a material, particularly an insulating material, having an open air-permeable structure and relatively thin cover boards and edge strips of a harder material which is substantially impermeable to air covering said core member on the opposed side faces and all edge faces thereof, respectively.
From an article by Christian Strobech "Bonding Lightweight Insulated Sandwich Elements with Polyurethane Adhesives" in the periodical ADHESIVES AGES, vol. 20, June 1977, pages 23 to 28, a method is known in which the partial vacuum or underpressure necessary to press cover boards into contact with a core member having uncovered edge faces is obtained by using a vacuum pressing table of a construction known per se with a table-top on which said members are positioned in a sandwiched arrangement in the prescribed order of succession upon a woven textile such as hessian, subsequent to application of adhesive to the cover boards. Thereafter, the sandwich structure is covered on the upper side with another piece of woven textile such as hessian, which is then covered by an air-impermeable plastic foil which is sealingly secured to the edges of the table top. Suction for providing the desired underpressure takes place through a number of stubs in the table top of the pressing table in the center line thereof. Thus, the flow path for the excavated air extends mainly through the uncovered edge faces of the core member and the woven material underneath the sandwich arrangement to said suction stubs.
In addition to the fact that vacuum pressing tables of this kind are relatively expensive per se, the operation thereof is complicated, so that exercise of the method described in the article requires considerable care and is relatively time-consuming, since the production of every single building element will require a number of operations. It appears also from the article that only 2 to 4 elements may be produced per pressing table within an eight-hour working day by the method described.
Since such a production capacity must be considered insufficient for industrial use, the article prescribes that in a more automatized production usual mechanical pressure application technology must be used.
However, particularly in the production of building elements of the kind mentioned in greater dimensions and with the use of recently developed, fast-curing adhesives, such as one-component polyurethane adhesives as suggested in the above mentioned article, it has appeared extremely difficult, when using mechanical pressure application technology, which for the production of elements of this kind is known inter alia from German patent specification No. 1,484,344, to obtain a sufficiently even pressure distribution during the curing of the adhesive and, thereby, an adhesive bond with sufficiently good strength characteristics. In addition, mechanical pressure application technology will require a considerable number of pressing stations in the same manner as the vacuum pressing technology suggested in the article, if a production capacity reasonable for industrial production is to be obtained.